Ion activity-measuring device and method for producing the same

ABSTRACT

The ion activity-measuring device of the present invention is provided with a hydrophobic bridge of which portion contacting with a liquid reservoir is hydrophilic. The hydrophobic bridge is made of, for example, at least one selected from the group consisting of polyester, nylon, polypropylene, rayon and polyethylene, and is produced by treating a portion contacting with the liquid reservoir with a spreading accelerator. The spreading accelerator is at least one selected from the group consisting of a surfactant and a hydrophilic polymer. There is also provided a method for producing the above ion activity-measuring device, comprising embedding nonwoven fabric in the cover plate to bond the nonwoven fabric to the cover plate.

TECHNICAL FIELD

The present invention relates to an ion activity-measuring device, whichis for measuring activity of an ion in a liquid sample such as blood,and a method for producing the same.

BACKGROUND ART

As a measurement device for measuring activity of an ion in a liquidsample by potentiometry, those utilizing dry-type electrodes are widelyused.

Such ion activity-measuring devices have at least one pair ofelectrodes, one of the electrodes being to contact with a liquid sample,and the other being to contact with a reference liquid. The electrode tobe contact with the liquid sample is usually imparted with anion-selective property. When a liquid sample and a reference liquid arebrought into contact with the electrodes, the potential differencegenerated between the electrodes depending on the difference of ionactivity is measured, and this potential difference is converted into aconcentration.

In order to generate such a potential difference, it is necessary toprovide electric conduction between the liquid sample and the referenceliquid, and this is realized by providing a bridge between a liquidreservoir for the liquid sample and a liquid reservoir for the referenceliquid.

Examples of such a bridge include the slit bridge formed by a Groovesuch as one disclosed in Japanese Patent Publication (Kokoku) No.58-4981, in the three-layer tri-laminate bridge made of a porous layerinserted between hydrophobic coating film layers such as one disclosedin Japanese Patent Publication No. 59-4659, the shield type bridge whichis a porous bridge composed of regions partitioned by shields that blockdiffusion of liquid such as one disclosed in Japanese Patent ApplicationLaid-Open (Kokai) No. 58-201056, the thread bridge made of twisted yamsuch as one disclosed in Japanese Patent Application Laid-Open No.58-211648 and so forth.

DISCLOSURE OF THE INVENTION

As a result of researches of the present inventors, it was found thatreproducibility of ion activity measurement utilizing the conventionaldevices still had a room for improvement.

Therefore, an object of the present invention is to provide an ionactivity-measuring device that can improve reproducibility of ionactivity measurement utilizing it.

The present inventors found that reproducibility of the ion activitymeasurement utilizing an ion activity-measuring device was improved byemploying a bridge of a specific structure in the ion activity-measuringdevice. Thus, they accomplished the present invention.

The present invention provides an ion activity-measuring device formeasuring activity of an ion in a sample, which comprises a hydrophobicbridge of which portion contacting with a liquid reservoir ishydrophilic (henceforth also referred to the “ion activity-measuringdevice of the present invention”).

In the ion activity-measuring device of the present invention, thehydrophobic bridge is preferably produced from at least one selectedfrom the group consisting of polyester, nylon, polypropylene, rayon andpolyethylene. Further, the hydrophobic bridge is preferably produced bytreating the portion contacting with the liquid reservoir with aspreading accelerator.

The spreading accelerator is preferably at least one selected from thegroup consisting of a surfactant and a hydrophilic polymer.

In one embodiment of the ion activity-measuring device of the presentinvention, the aforementioned liquid reservoir is formed by bonding acover plate and a substrate, at least one of which has a resist filmhaving a liquid reservoir form, and the aforementioned hydrophobicbridge is made of nonwoven fabric.

The present invention also provides a preferred method for producing theion activity-measuring device of the present invention according to theaforementioned embodiment. This production method comprises embeddingthe nonwoven fabric in the cover plate to bond the nonwoven fabric to,the cover plate. The nonwoven fabric and the cover plate are preferablybonded by ultrasonic fusion, more preferably knurling fusion.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 shows an exploded perspective view of an ion activity-measuringdevice.

FIG. 2 is a plan view of an exemplary structure of a cover plate havinga bridge.

FIG. 3 is a sectional view along the line III—III in FIG. 2.

FIG. 4 is a plan view of an exemplary structure of a cover plate havinga bridge.

FIG. 5 is a sectional view along the line V—V in FIG. 4.

FIG. 6 is a plan view of an exemplary structure of a cover plate havinga bridge.

FIG. 7 is a sectional view along the line VII—VII in FIG. 6.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, embodiments of the present invention will be explained indetail.

The ion activity-measuring device of the present invention measures ionactivity based on the potentiometry. That is, the ion activity-measuringdevice of the present invention has at least one pair of electrodes, andwhen a sample and a reference liquid contact with the electrodes, apotential difference is generated between the-electrodes depending onthe difference of ion activity. This potential difference is convertedinto the activity based on a calibration curve.

As the sample, liquid samples such as whole blood, blood serum, bloodplasma and urine can be mentioned.

The ion activity-measuring device of the present invention can beconstituted as a conventional ion activity-measuring device usingdry-type electrodes except that it has a bridge of the specificstructure.

Such an ion activity-measuring device generally comprises a firstelectrode, a first liquid reservoir which is disposed on the firstelectrode, a second electrode, a second liquid reservoir which isdisposed on the second electrode, and a bridge that can provideselectric conduction between the first liquid reservoir and the secondliquid reservoir. It is stored in a dry state, and once a liquid sampleand a reference liquid are put into the two liquid reservoirs when thedevice is used, electric conduction is attained between the first liquidreservoir and the second liquid reservoir by the bridge.

The electrodes can be formed by providing, on a substrate, metal layersfor electrodes of a pattern composed of an electrode portion contactingwith a liquid sample or a reference liquid, a terminal portion forelectrically connecting with an apparatus for ion activity measurementand a lead wire portion connecting the electrode portion and theterminal portion; forming a resist film by printing or the like so thatthe electrode portion should be defined; chemically treating theelectrode portion of each of the metal layers to form a metal saltlayer; and providing an electrolyte layer and an ion selective film oneach electrode portion defined by the resist film as required. Two ormore of electrode pairs which each are composed of the first electrodeand the second electrode may be provided.

As the substrate, a film or sheet of an insulating material, forexample, a plastic film is used. As the plastic, polyester,polypropylene, acrylate resin, vinyl chloride resin and so forth arepreferred.

As the metal for electrodes, metals such as silver, gold, platinum andpalladium can be used, and silver is preferred. The electrode metallayer can be formed by a usual method, for example, screen printingutilizing a metal paste, metal vapor deposition and so forth.

The resist film is a layer made of an insulating material, and it isformed so that it should cover the portions other than the electrodeportions and the terminal portions. When the electrolyte layer and theion selective film are formed on the electrode portions in thesubsequent steps, the resist film acts as a “wall” defining them. The“wall” is advantageously positioned outside the outer peripheries of theelectrode portions by 0.2 to 1.0 mm to provide a gap, in order to form auniform ion-selective film (refer to Japanese Patent ApplicationLaid-Open No. 2-287146). By providing a non-conductive portion at thecontact portion of the resist film and the electrode portions beforeforming the resist film, the same effect can be obtained as obtained byproviding a gap between the Mwallo and the electrode portions. Althoughcommercially available insulating inks and so forth can be used as amaterial of the non-conductive portion, non-conductive metal pastes arepreferred in views of adhesive property, etching resistance and soforth. The non-conductive paste means a metal paste containing metal atsuch a content that the metal paste should not become substantiallyconductive.

While the material of the resist film is not particularly limited solong as it is an insulating material, commercially available insulatinginks can be used. Examples thereof include those of ultraviolet curingtype, for example, ML25089, ML25094 and ED450SS (trade names) producedby Acheson Japan, STR5320 (trade name) produced by Sinto Chemitron, DS-4and INS-3 (trade names) produced by Jujo Chemical, FOC-3S (trade name)produced by Taiyo Ink Mgf., those of thermosetting type, for example,STR-5110 (trade name) produced by Sinto Chemitron, HIPET9300 (tradename) produced by Jujo Chemical, CR420G and CR48G (trade names) producedby Osaka Asahi Chemical and so forth.

When an ultraviolet curing type insulating ink is used, the resist filmcan be obtained by applying the insulating ink by screen printing, thencuring it by ultraviolet irradiation using a UV irradiation machine, andrepeating such procedure until a predetermined thickness is obtained.When a thermosetting type insulating ink is used, it may be heated to100 to 150° C. instead of the ultraviolet irradiation.

The electrode portions defined by the resist film are chemically treatedto form a metal salt layer on the metal surface. Before applying theresist, the metal terminal portions may be masked and chemicallytreated. The metal salt is usually a halide, preferably a chloride.However, other salts may also be used.

Then, the electrolyte layer and the ion-selective film are formed oneach of the electrode portions utilizing the regions surrounded by theresist film. The electrolyte layer may not be used as the electrodedisclosed in Japanese Patent Application Laid-Open No. 57-106852.

When an electrolytic solution is poured into this region, a liquid filmof a substantially uniform thickness can be formed on the electrode bysurface tension. Therefore, by drying the liquid without disturbing theliquid, an electrolyte layer of a uniform thickness can be formed atleast on the reference electrode. Although the electrolyte is preferablyone containing anions of the same species as that of the aforementionedmetal salt, it may be one containing different anions, or an electrolytelayer not containing electrolyte may be formed only with a polymer.

Further, by pouring a solution of a material of the ion-selective filmon the electrolyte layer and drying it, an ion-selective film of auniform thickness can similarly be formed. The material of theion-selective film may be a known one, for example, the hydrophobicion-selective film material disclosed in Japanese Patent Publication No.58-4981 can be used. When two or more electrode pairs are provided,different kinds of the ion-selective film materials can be used for theelectrode pairs, and thus it is enabled to simultaneously measureactivities for two or more kinds of ions.

The liquid reservoir is not particularly limited, so long as it canretain a measurement sample or a reference liquid on the electrodes. Itmay be a well formed by an insulating material, or a space formed by twoor more laminated insulating materials. Preferably, a resist film havinga liquid reservoir form is formed on a cover plate composed of aninsulating material film provided with a sample-feeding hole, a airventilation hole, a bridge hole and holes for exposure of terminals, andthe resist film is bonded to a substrate on which the aforementionedion-selective film has been formed to form a liquid reservoir with theresist film of the substrate, the cover plate and the resist film of thecover plate. The ion activity-measuring device that has such a liquidreservoir can be in a plate-like form, and it is preferred as adisposable ion activity-measuring device.

On the side of the electrodes of the ion activity-measuring device,there may be provided a protective film that can be easily peeled uponuse. Further, indication of the mounting direction on an apparatus forion activity measurement may be printed. Furthermore, on the backsurface, identification codes such as bar codes may be printed.

The ion activity-measuring device of the present invention comprises ahydrophobic bridge of which portion contacting with a liquid reservoiris hydrophilic. This bridge may be hydrophilic for the entire portioncontacting with a liquid reservoir, or only a part of it, i.e., a tipend of it may be hydrophilic.

While a member constituting the hydrophobic bridge is not particularlylimited so long as a liquid can permeate it, examples thereof includeporous members such as nonwoven fabric and textile fabric. Examples of amaterial of the member constituting the bridge include a hydrophobicpolymer. This material is preferably one which can be fused to the coverplate. Specific examples of the hydrophobic polymer are polyesters(e.g., polyethylene terephthalate), nylon, polypropylene, rayon,polyethylene and so forth.

The bridge having the above structure can be produced by treating theportion contacting with the liquid reservoir with a spreadingaccelerator. Alternatively, it can also be constituted by a hydrophobicporous member and hydrophilic porous members that are disposed on theboth sides of the hydrophobic porous member so that they should be incontact with the hydrophobic porous member. In view of the simplicity ofthe production method, the portion contacting with the liquid reservoiris preferably constituted by the hydrophobic porous member treated withthe spreading accelerator.

The spreading accelerator is not particularly limited, so long as thehydrophobic polymer can be made hydrophilic by treatment with it.Examples thereof include a surfactant and a hydrophilic polymer. As thesurfactant, it is preferable to use a nonionic surfactant in view of theinfluence on the measurement of ion activity. When the measurement isperformed for a sample containing blood cells, it is preferable to use anonionic compound such as Triton X-405 (trade name) and lecithin, whichexhibit little influence such as disruption of the blood cells. As thehydrophilic polymer, it is possible to use polyvinyl alcohol orpolyvinylpyrrolidone (e.g., PVPK15 (trade name)). The surfactant and thehydrophilic polymer may be used each alone or in combination. Further,one kind of each may be used or two or more kinds of each may be used incombination.

The treatment with the spreading accelerator can be performed by soakingthe both ends of the bridge with a solution of the spreading acceleratorin a suitable solvent by spraying, coating, dipping, point depositionetc., and drying it. By the treatment with the spreading accelerator,the treated portion is made hydrophilic. The amount of the spreadingaccelerator required for imparting the hydrophilicity can be easilydetermined by those skilled in the art.

The bridge having the above structure is preferably bonded to the coverplate by fusion using an ultrasonic fusion machine. In this case, byusing an ultrasonic fusion machine having a knurled horn tip end,bonding of further higher adhesion strength can be attained.

The reason why the reproducibility of the ion activity measurementmethod utilizing the ion activity-measuring device of the presentinvention is improved is presumed as follows. Since conventional bridgesare constituted by a uniform material along the direction of liquidpermeation, the fronts of the liquids permeated from the first liquidreservoir and the second liquid reservoir are not uniform in many cases,and this is considered to invite partial contact or mixing of theliquids. On the other hand, in the bridge of the ion activity-measuringdevice of the present invention, since a 3-part structure of hydrophilicportion/hydrophobic portion/hydrophilic portion is formed between thefirst liquid reservoir and the second liquid reservoir along thedirection of liquid permeation, the liquids on the both liquidreservoirs permeate into the hydrophilic portions first, but do notreach the center portion at once due to the hydrophobicity of the centerportion. Then, after a sufficient amount of the liquids are retained inthe hydrophilic portions, the liquids advance toward the hydrophobicportion at a stretch and the both liquids are brought into contact witheach other. For this reason, it is considered that, in the ionactivity-measuring device of the present invention, there are suppressedthe partial contact and mixing of the liquids, which are considered toadversely affect the reproducibility of ion activity measurement, andthus the reproducibility is improved.

Hereafter, an ion activity-measuring device of plate-type will beexplained as an example of the ion activity-measuring device of thepresent invention with reference to FIG. 1. FIG. 1 is an explodedperspective view of the ion activity-measuring device In this ionactivity-measuring device, a substrate 1, on which electrode metallayers constituting three pairs of electrodes and each composed of anelectrode portion 2, a terminal portion 3 and a lead wire portion 4, afirst resist film 5 and an ion-selective film are formed, is adhered toa cover plate 7 composed of a film of an insulating material providedwith a sample-feeding hole 8, an air ventilation hole 9 and holes forexposure of terminals 10, on which a second resist film 6 is formed,whereby liquid reservoirs are formed with the first resist film 5, thecover plate 7 and the second resist film 6.

Examples of the structure of the cover plate having a bridge is shown inFIGS. 2 to 7. FIGS. 2, 4 and 6 are plan views, and FIGS. 3, 5 and 7 aresectional views along the lines of III—III, V—V and VII—VII in FIGS. 2,4 and 6, respectively.

In the example shown in FIG. 2, nonwoven fabric or textile fabric isdisposed as a bridge material (porous member) so as to cover a hole forbridge 11, and fused to the cover plate 7. Referring to FIG. 3, aportion of the nonwoven fabric or textile fabric contacting with thecover plate 7 is fused, and the portion not fused due to the presence ofthe hole for bridge 11 serves as a bridge 12.

The width b of the hole for bridge should be larger than the width of aseparator that is a portion separating the first liquid reservoir andthe second liquid reservoir of the second resist, so that flows ofliquids from the liquid reservoirs should not be prevented.

In the example shown in FIG. 2 where the air ventilation hole 9 iscommonly used for the first liquid reservoir and the second liquidreservoir, the width of the air ventilation hole is wider than the widthof the separator of the second resist 6.

The air ventilation hole 9 may also be provided for each of the firstliquid reservoir and the second liquid reservoir as shown in FIG. 4. Inthis case, the size of the air ventilation hole 9 need not be largerthan the width of the separator of the second resist 6.

Further, as shown in FIG. 6, the air ventilation hole 9 may also serveas the hole for bridge. In this embodiment, the bridge 12 is disposed sothat it should cover a part of the area of the air ventilation hole 9and thus the air ventilation of the liquid reservoirs should bepossible.

The fusion of the nonwoven fabric or textile fabric to the cover plate 7can be attained by ultrasonic wave or heating. The length to be fused ofthe nonwoven fabric or textile fabric used for the bridge 12 may be thesame as that of the plate as shown in FIGS. 2 or 4, or it may be a partof the length as shown in FIG. 6. However, it should be longer than thesize of the hole for bridge. The thickness of the nonwoven fabric ortextile fabric is usually 30 to 200 μm, more preferably 50 to 150 μm.

Further, a commonly used hole for bridge as shown in FIG. 6 may be usedwith nonwoven fabric or textile fabric fused over the full length of theplate as shown in FIG. 2 or 4, or a independent hole for bridge as shownin FIG. 2 or 4 may be used with nonwoven fabric or textile fused for apartial length as shown in FIG. 6.

As for the aforementioned bridge material, when the spreading of liquidshows anisotropy in it, mixing state and mixing rate of a standardliquid (reference liquid) and a measurement liquid (liquid sample) inthe bridge, which are important factors for stability of electricresponse potential, can be controlled by selecting the direction of thefusion of the material.

An example of the method for producing an ion activity-measuring devicewill be explained with reference to FIG. 1.

First, as shown in FIG. 1(a), a conductive metal paste (preferablysilver paste) is applied to the substrate 1 made of a plastic film by aconventional method such as printing to form metal layers of anelectrode pattern composed of an electrode portion 2, a terminal portion3 and a lead wire portion 4 connecting the electrode portion 2 and theterminal portion 3. A portion to be the electrode portion 2 may beconverted into silver halide by chemical treatment in this stage, butsuch chemical treatment is preferably performed after the first resistfilm S is formed. If a layer of a non-conductive material is provided atthe contact portion of the metal layer for electrode and the firstresist film 5 (i.e., a portion around the electrode portion 2) beforeforming the first resist film 5, it will be advantageous for forming auniform ion-selective film.

Then, on the substrate 1 on which the metal layers for electrode areformed, the first resist layer 5 in a form covering portions other thanthe electrode portions 2 and the terminal portions 3, as shown in FIG.1(b), is formed.

In this stage, a predetermined amount of a solution of the ion-selectivefilm material is poured into the regions surrounded by the first resistlayer 5 over the electrode portions 2, and dried to form ion-selectivefilms. The ion-selective films are formed on the right and left sides asone pair. In the device shown in the figure, the ion-selective films areformed to contain three kinds of ion carriers. Before the ion-selectivefilms are formed, a predetermined amount of an electrolyte solution maybe poured into the regions surrounded by the first resist layer 5 overthe electrode portions 2, and dried to form electrolyte layers, and thenthe ion-selective films may be formed on the formed electrolyte layers.

Separately, a cover plate 7 composed of a plastic film provided with asample-feeding hole 8, an air ventilation hole 9 and holes for exposureof terminals 10 is prepared as shown in FIG. 1(d), and ribbon-shapednonwoven fabric made of a hydrophobic polymer is fused to the coverplate so that the nonwoven fabric should cross the air ventilation hole9, which also serves as a bridge hole.

On this cover plate 7, the second resist layer 6 in such a form that itshould form two liquid reservoirs each containing one of a pair of theelectrode portions 2 as shown in FIG. 1(c) is formed. The width of the,portion separating two liquid reservoirs (separator) is selected to benarrower than the diameter of the air ventilation hole 9.

A solution of a spreading accelerator is sprayed on the surface providedwith the second resist layer 6 so that the exposed nonwoven fabricportion should become hydrophilic, and the surface is dried. As aresult, a bridge is formed.

The second resist layer 6 side of the cover plate 7 obtained asdescribed above and the first resist layer 5 side of the substrate l onwhich the aforementioned ion-selective film is formed are adhered tocomplete the ion activity-measuring device of the present invention.While the above procedure was explained without especially referring tonumber of the device, a pattern comprising a plurality of ionactivity-measuring devices can be formed on one sheet of film accordingto the size that can be printed by a screen printing machine or thelike. In such a case, by cutting the film in a final step, a plural ofion activity-measuring devices of the present invention can be producedsimultaneously.

Upon measurement, a liquid sample of which ion activity is to bemeasured and a reference liquid of a predetermined ion activity aresupplied from one of sample-feeding holes and the other, respectively,substantially at the same time. The supplied liquid sample and thereference liquid spread over the entire volume of the spaces formed bythe cover plate, the first resist layer and the second resist layer(liquid reservoirs) by capillarity, contact with each electrode, andpermeate the bridge to provide electric conduction between the bothliquid reservoirs.

As a result, an electric cell is formed between each pair of theelectrodes. Its electromotive force can be measured and a concentrationcan be calculated based on a calibration curve prepared beforehand.

In a preferred method for producing the ion activity-measuring device ofthe present invention, a porous member is provided on a member whichconstitutes a liquid reservoir and has a hole for bridge; a separator isprovided thereon so that the separator should cross over the hole forbridge; and then a spreading accelerator is sprayed to treat an exposedportion of the porous member with the spreading accelerator to form abridge.

The member that has the hole for bridge is usually the aforementionedcover plate. The separator is a member for separating the first liquidreservoir and the second liquid reservoir, and usually formed as a partof the second resist. By spraying the spreading accelerator after theseparator is provided, only the both ends of the porous member aretreated with the spreading accelerator, and a three-part structure ofhydrophilic part/hydrophobic part/hydrophilic part can easily beobtained. Therefore, this production method is suitable for massproduction of the ion activity-measuring device of the presentinvention.

Further, it is preferable to form a bridge by disposing a porousmaterial of a ribbon-like shape (bridge material) for the full length ofthe plate, and fusing it to the cover plate. When the ionactivity-measuring devices of the present invention are produced in alarge scale by cutting out from one sheet of film in a final stepaccording to this embodiment, the positioning and fusion of the porousmaterial become easy according to this embodiment. Therefore, massproduction becomes easy.

In an embodiment of the ion activity-measuring device of the presentinvention, i.e., an embodiment where liquid reservoirs are formed bybonding a cover plate and a substrate, at least one of which has aresist film having a liquid reservoir form, and the hydrophobic bridgeis made of nonwoven fabric, the nonwoven fabric in the shape of a sheet,produced from polyester, nylon, polyvinylene, rayon, polyethylene or thelike, as a member constituting the hydrophobic bridge is bonded to thecover plate.

For the bonding in this case, while heat fusion attained by heating orbonding with an adhesive may be generally used, the nonwoven fabric ispreferably embedded in the cover plate to bond the nonwoven fabric tothe cover plate.

The bonding of the cover plate and the nonwoven fabric is attained byoverlaying the nonwoven fabric on the cover plate. When heat fusion isused for the bonding, the overlapped portion has a structure having athickness of the nonwoven fabric, and therefore it has a leveldifference with respect to the cover plate. When an adhesive is used forthe bonding, the thickness of the applied adhesive is added to thethickness of the nonwoven fabric itself.

The liquid sample and the reference liquid are each added to separateliquid reservoirs to fill the liquid reservoirs with the liquids. Sincethe liquid sample and the reference liquid are added at a relativelyhigh speed by using a pipet or the like, an air layer may be formed atthe portion having the level difference between the cover plate and thenonwoven fabric. Thus, there may be observed a phenomenon that theliquid sample and the reference liquid are not spread over the bridge,or they are difficult to spread.

Further, if the cover plate and the nonwoven fabric are bonded only byheat fusion, the nonwoven fabric may be easily peeled when a force isapplied to the fused portion. Therefore, there is also a risk that thebridge may be peeled due to drop thereof during transportation or use ofthe device for ion activity measurement, and thus the device becomesunusable.

If the nonwoven fabric is embedded in the cover plate and bonded to it,the level difference between the cover plate and the bridge is reduced.Thus, an air layer is not formed upon addition of the liquid sample andreference liquid, and bonding strength is also improved. Therefore, theaforementioned problem can be solved.

In order to embed the nonwoven fabric in the cover plate, it iseffective to attain the bonding by heating and pressing the portionoverlapped with the nonwoven fabric to push the thickness of thenonwoven fabric into the cover plate as much as possible.

As such a bonding method, there can be mentioned a heat fusion. The heatfusion includes the heating fusion method, ultrasonic fusion method andhigh frequency fusion method. In these methods, bonding is attained bydirectly applying heat or generating heat to melt a member to be fused,and applying a certain level of pressure.

The heating fusion method is a method for bonding by directly applyingheat to a part to be fused. Since the heat is applied to a portion otherthan the portion desired to be fused in this method, it requires certainmeans for preventing distortion of the cover plate upon pressing.

The high frequency fusion method is a method for bonding by vibratingmetal particles of aluminum or the like present in the member to befused to generate heat and melting the member by the generated heat.This method is required to prepare nonwoven fabric or a PET film bymixing metal particles such as those of aluminum.

Therefore, the preferred fusion method for the present invention is theultrasonic fusion method. In the ultrasonic fusion, bonding is attainedby using a horn conducting a supersonic wave, which is brought intocontact with a portion to be fused to melt a member to be fused at eachsurface.

Most preferably, bonding is attained by knurled fusion based on theultrasonic fusion.

The knurled fusion is a bonding method in which a knurled horn providedat the tip end of a fusion machine is used; a knurled portion vibratedwith an ultrasonic wave melts a member to be fused; and a certain levelof pressure is applied. Thus, a surface of the member to be fusedcontacting with the knurled portion is finished to have a knurledpattern.

While the nonwoven-fabric can be embedded in the cover plate by suchbonding as described above, the entire nonwoven fabric is not necessaryto be embedded in the cover plate, and it may be sufficient if there isobtained the effect of facilitating spreading of the liquid sample andthe reference liquid by reducing the level difference due to thethickness of the nonwoven fabric.

The bonding strength between the fused cover plate and nonwoven fabricmay vary depending on the thickness. In order to maintain the strength,the thickness of the cover plate is preferably 50 to 250 μm, and thethickness of the nonwoven fabric is preferably 30 to 150 μm.

EXAMPLES

Hereafter, the present invention will be specifically explained withreference to the following examples.

Example 1

An ion activity-measuring device for simultaneously measuring each ofNa, K and Cl ions was prepared by the following process steps.

Step 1. Patterns each composed of an electrode portion, a terminalportion and a lead wire portion connecting the electrode portion and theterminal portion were printed with a thermosetting silver paste (VO-200,produced by Acheson Japan) through a screen of 200 mesh with a thicknessof 20 μm on a polyester film so as to form three pairs of electrodes,and then the paste was cured by heating at 150° C. for 30 minutes toform silver layers.Step 2. An ultraviolet curing type resist,(ML-25089, produced by AchesonJapan) was printed on the contact portions of a resist film and theelectrode portions through a screen of 300 mesh and a thickness of 10 μmand cured by ultraviolet radiation.Step 3. An ultraviolet curing type resist was printed on portions otherthan the terminal portions and electrode positions through a screen of300 mesh and a thickness of 40 μm and cured by ultraviolet radiation.This procedure was repeated 3 times to form a resist film with athickness of about 50 μm.Step 4. The polyester film was immersed in 3 N nitric acid aqueoussolution for 1 minute and washed.Step 5. The polyester film was immersed in a chromic acid solution (1%dichromic acid, 0.15 N hydrochloric acid, 0.2 N potassium chloride) for3 minutes and washed to form a silver chloride layer.Step 6. A solution of each ion-selective film material, of whichcomposition is shown in Table 1, was added dropwise to holes in anamount of 0.7 μl per hole and dried to form an ion-selective film.

TABLE 1 Composition of ion-selective film Na K Cl Polyvinyl chloride(Aldrich) 8.00 8.00 8.00 Dioctyl adipate (Wako Pure 27.00  28.00  17.00 Chemicals) NaTFPB1¹⁾ (Dojin Chemical) 0.05 B124²⁾ (Dojin Chemical) 0.60KTCPB³⁾ (Dojin Chemical) 0.05 Valinomycin (Calbiochem) 0.35 Capriquat⁴⁾(Dojin Chemical) 8.00 Tetrahydrofuran (Nakarai Tesque) 64.35  63.60 67.00  ¹⁾Sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate²⁾Bis[(12-crown-4)methyl]-2-dodecyl-2-methylmalonate ³⁾Potassiumtetrakis(p-chlorophenyl)borate ⁴⁾Tri-n-octylmethylammonium chlorideStep 7. A polyester film provided with a sample-feeding hole, an airventilation hole, holes for exposure of terminal portions and a bridgehole was prepared, and polyethylene terephthalate nonwoven fabric(MF-80K (trade name), produced by Japan Vilene, thickness: 100 μm) wasdisposed over the bridge hole and fused.

As the nonwoven fabric, nonwoven fabric in a ribbon-like shape having athickness of 100 μm and a width of 2 mm was used. The polyester film wasmade of polyethylene terephthalate, and had a thickness of 188 μm and asize of 16×17 cm.

After the ribbon-like nonwoven fabric was fitted approximately on thecenter of the bridge hole, the polyester film and the nonwoven fabricwere fused by using an ultrasonic fusion machine, Branson UltrasonicWave Plastic Assembly System 947D (produced by Emerson Japan, fusionconditions: frequency of 40 kHz, fusion time of 0.12 seconds andpressure of 1.0 kgf/cm²).

The tip end of a horn used for the aforementioned ultrasonic fusionmachine was one subjected to knurling with a size of 0.3 mm (mesh) foran area of 24×5 mm.

Step 8. An ultraviolet curing type resist was printed in a pattern forforming liquid reservoirs through a screen of 300 mesh with a thicknessof 40 μm and cured by ultraviolet radiation. This procedure was repeated3 times to form a resist film with a thickness of about 50 μm.Step 9. A solution of a surfactant and a hydrophilic polymer.(water:Triton X-405:PVPK15=98.5:1.0:0.5 (weight ratio)) was sprayed onthe surface of the polyester film on which the resist film had beenformed in an amount of 1.0 mg/cm², and the polyester film was dried,whereby only the portions of the bridge not covered by the resist filmwere treated with the surfactant and the hydrophilic polymer.Step 10. The polyester films obtained in the above 6 and 9 were bondedand cut into a predetermined size to obtain an ion activity-measuringdevice.

Example 2

An ion activity-measuring device was obtained in the same manner as inExample 1 except that the process step 7 in Example 1 was modified asfollows.

Step 7. A polyester film provided with a sample-feeding hole, an airventilation hole and holes for exposure of terminal portions wasprepared, and polyethylene terephthalate nonwoven fabric in aribbon-like shape (MF-80K (trade name), produced by Japan Vilene.,thickness: 80 μm) was fused so that it should cross the air ventilationholes for each electrode to form a bridge.

Comparative Example 1

An ion activity-measuring device was obtained in the same manner as inExample 1 except that the process step 9 was not performed.

Comparative Example 2

An ion activity-measuring device was obtained in the same manner as inExample 1 except that silk twisted yarn (Y-KT2510 (trade name), producedby Kyo Sakura, diameter: 80 μm) was used as the material of the bridgeand the process step 9 was not performed.

Test Example

The measurement of ion activity of human blood serum was performed byusing an electrode type electrolyte analyzer (Spotchem (trade mark)SE-1510, Kyoto Dai-ichi Kagaku) equipped with one of the ionactivity-measuring devices obtained in Examples 1 and 2 and ComparativeExamples 1 and 2. The measurement was performed 7 times, andstandard-deviations (S.D.) and variation of electric potential wereobtained. The results are shown in Table 2.

TABLE 2 Measured values for 60 seconds Variation of electric S.D.potential (mV) Na K Cl Na K Cl Example 1 0.16 0.13 0.20 0.46 0.42 0.56Example 2 0.18 0.15 0.19 0.48 0.42 0.52 Comparative 0.53 0.28 0.41 1.540.78 1.20 Example 1 Comparative 0.24 0.19 0.25 0.68 0.60 0.72 Example 2

As clearly shown by the above results, when the ion activity-measuringdevices of the present invention were used, the standard deviation andthe variation o,f electric potential were smaller. Thus, it have beenfound that the reproducibility of the ion activity measurement using theion activity-measuring device of the present invention is excellent.

Industrial Applicability

According to the ion activity-measuring device of the present inventionutilizing dry-type electrodes, ion activity can be measured with goodreproducibility. Further, according to the ion activity-measuring deviceof the present invention, the,production method therefor can besimplified and it can be readily produced in an integrated productionline. Therefore, it enables cost reduction.

1. An ion activity-measuring device for measuring activity of an ion ina sample, which comprises at least one pair of electrodes, one of theelectrodes being to contact with a liquid sample, and the other being tocontact with a reference liquid, a first liquid reservoir for the liquidsample, a second liquid reservoir for the reference liquid, and ahydrophobic bridge of which portions contacting with the liquidreservoirs are hydrophilic, wherein the device is adapted to supplyingthe liquid sample and the reference liquid substantially at the sametime, and wherein the hydrophobic bridge is produced by treating theportions contacting with the liquid reservoirs with a spreadingaccelerator.
 2. The ion activity-measuring device according to claim 1,wherein the hydrophobic bridge is produced from at least one selectedfrom the group consisting of polyester, nylon, polypropylene, rayon andpolyethylene.
 3. The ion activity-measuring device according to claim 1,wherein the spreading accelerator is at least one selected from thegroup consisting of a surfactant and a hydrophilic polymer.
 4. The ionactivity-measuring device according to claim 1, wherein the liquidreservoirs are formed by bonding a cover plate and a substrate, at leastone of which has a resist film having a liquid reservoir form, and thehydrophobic bridge is made of nonwoven fabric.
 5. A method for producingthe ion activity-measuring device as defined in claim 4, comprisingembedding nonwoven fabric in the cover plate to bond the nonwoven fabricto the cover plate.
 6. The method according to claim 5, wherein thenonwoven fabric and the cover plate are bonded by ultrasonic fusion. 7.The method according to claim 5, wherein the nonwoven fabric and thecover plate are bonded by knurling fusion.